First off What is Lymphoma?
We have to first define what lymphoma is before discussing Hodgkin's disease. Lymphoma is a cancer that develops from cells in the body known as "lymphocytes." Lympocytes are a subcategory of white blood cells. There are two different types of lymphocytes: B-cells and T-cells. Almost all lymphomas, including Hodgkin's disease, stem from B-cells.
In Hodgkin's lymphoma a B-cell, for unknown reasons, becomes cancerous. The cell then makes many many clones of itself. These cells bundle together to form a solid tumor known as a lymphoma. There are several hypotheses for why these cells become cancerous in Hodgkin's. One belief is that infection with Epstein-Barr virus (EBV, the same virus that causes infectious mononucleosis) can cause the cells to turn malignant in genetically susceptible people. Other theories are that certain genetic translocations may be the underlying factor. As of yet, no particular theory has significant supporting data to call it the "cause." In fact, there may be multiple unrelated causes.
There are different subcategories of Hodgkin's lymphoma. They are based on several microscopic characteristics, and are important in determining prognosis. The features the pathologist is looking for are the number of Reed-Sternberg cells, as well as the number of lymphocytes present in the biospy specimen. A Reed-Sternberg cell is a funny shaped cell with two nuclei that looks like owl's eyes.
The first subcategory, and most common type, is nodular sclerosing Hodgkin's lymphoma. In this type there are very few Reed-Sternberg cells with a moderate number of lymphocytes. It commonly occurs in younger individuals, and with treatment, the prognosis is excellent.
The second subcategory is mixed cellularity Hodgkin's lymphoma. This type has many Reed-Sternberg cells and a moderate number of lymphocytes when viewed under the microscope. It has an intermediate prognosis.
The third subcategory is lymphocyte predominant Hodgkin's. It has very few Reed-Sternberg cells and many lymphocytes. It occurs most commonly in males less than 35 years of age. It is also one of the few types that is not associated with Epstein-Barr virus infection.
The last subcategory is lymphocyte depleted. It is the rarest form of Hodgkin's lymphoma. It typically affects older males. Unfortunately it has the worst prognosis of the four types.